Hearing assistance devices include a variety of devices such as assistive listening devices, cochlear implants and hearing aids. Hearing aids are useful in improving the hearing and speech comprehension of people who have hearing loss by selectively amplifying certain frequencies according to the hearing loss of the subject. A hearing aid typically has three basic parts; a microphone, an amplifier and a speaker. The microphone receives sound (acoustic signal) and converts it to an electrical signal and sends it to the amplifier. The amplifier increases the power of the signal, in proportion to the hearing loss, and then sends it to the ear through the speaker. Cochlear devices may employ electrodes to transmit sound to the patient.
A tone language like Mandarin, Cantonese or Thai is unlike English, because tone language relies on pitch discrimination for speech intelligibility. For example, Mandarin uses four tones to clarify the meanings of words: a first tone at a high level, a second rising tone, a third falling then rising tone, and a fourth falling tone. An example is shown in the table of FIG. 4. Since many characters have the same sound, tones are used to differentiate words from each other. The tones are discriminated by the pitch changes which are often limited to a small range in the low frequency spectrum.
For hearing-impaired listeners, even with the aid of a hearing assistance device, the pitch detection rate could drop due to insufficient spectrum resolution and hearing loss in low frequencies. This leads to poor speech intelligibility of a tone language for a wearer of a hearing assistance device.
Thus, there is a need in the art for an improved method and apparatus for enhancing tone language for hearing assistance devices.